1. Field of the Invention
The present invention relates to a rotary electric machine having a Lundell type pole core which is composed of a plurality of claw poles.
2. Description of the Related Art
Usually, an alternator for a vehicle has a Lundell type pole core which is composed of a plurality of claw poles. When the alternator is operated at a high speed, the centrifugal force is applied to the claw poles, and the tip of the claw poles may expand in the radial direction if the rotation speed of the alternator rotor becomes very high. This may cause the magnetic noises also.
In order to prevent the expansion of the claw poles, JP-A-59-226645 and JP-U-56-102983 propose a dumper ring fixed to the inside radial surface of the claw poles. JP-U-56-101185 proposes a ring having a trapezoidal cross-section inserted in a groove formed on the outer periphery of the claw poles. The groove has the same trapezoidal cross section. JP-A-4-165950 discloses a rotor which has claw poles covered by a cylindrical stainless member. JP-A-6-78479 discloses a pair of fans having ring members engaging the tip of the claw poles. JP-A-7-312854 discloses non-magnetic protection plates which are inserted between the claw poles and welded to side walls of the claw poles.
However, JP-A-59-226645 and JP-U-56-102983 can not suppress magnetic noises sufficiently because the dumper ring is fixed to the inside surface of the claw poles. The outer periphery of the pole core disclosed in JP-U-56-101185 needs a considerably large groove which has a trapezoidal cross-section. In this structure, the tip portion of the claw poles is not fixed, thereby allowing expansion. The stainless cylindrical member disclosed in JP-A-4-165950 increases the air gap between the stator and the pole core, thereby reducing the output power thereof. The fan disclosed in JP-A-6-78479 becomes complicated and difficult to manufacture. The protection plates of JP-A-7-312854 necessitate many welding steps.